Have been using UrBackup for a while (on Windows and Linux) but haven’t seen am option of only backing up when the client is locked…
That said, from my experience, there isn’t much change in performance when backups are running - the only thing that I’ve noticed was when an image was being taken, while I was on a VOIP call, while working wirelessly…and it was a little glitchy a few times during the call; this hasn’t been a noticeable issue when working with a network cable connected though…